1. Field of the Invention
This invention relates to electronic tone synthesis and in particular is concerned with a means for imitating a guitar-like instrument on a keyboard musical instrument.
2. Description of the Prior Art
Contemporary keyboard electronic musical instruments are capable of producing a fair imitation of the sounds produced by plucked stringed instruments. Such plucked instruments include the guitar, mandolin, banjo, ukelele as well as the classic harpischord. A problem that exists is not primarily of imitating the sounds produced by plucked stringed musical instruments, but rather the problem is that encountered in attempting to play a keyboard instrument in a fashion that is imitative of the sounds produced by strumming a fretted stringed musical instrument such as a guitar. The term "guitar" is used in a generic sense to denote a class of stringed musical instruments having a multiplicity of strings that are plucked or strummed in a sequential order.
A musician performing on a guitar divides the required dexteral skill between two hands. One hand is used to select a chord by pressing a subset of the strings against prepositioned frets. The other hand is occupied with plucking or strumming the strings.
The playing situation is generally quite different and more difficult on an electronic keyboard instrument if one attempts to imitate a guitar. The musician is forced to input all the note and keying data with a single hand. The second hand and feet are presumed to be occupied as they are usually dedicated to providing the accompaniment to the solo lines which imitate the guitar sounds. Since a guitar, for example, has six strings the musician is faced with a compatability problem of six strings versus five fingers on one hand. A further problem arises because two of the strings on a guitar are bass strings. The six open strings of a guitar are tuned to E.sub.2, A.sub.2, D.sub.3, G.sub.3, B.sub.3 and E.sub.4. This two octave range of notes cannot be played on a standard piano-type keyboard with a single hand.
Aside from the preceding problems of keying the notes on a keyboard to imitate a guitar, there is an additional problem of properly keying the sounds. Stringed instruments of the guitar generic type can be played in a wide variety of different modes. Two principal playing modes predominate most performances. The first is the solo mode in which only a single string is plucked at a time to sound a melodic line. The solo mode is readily imitatable with a keyboard electronic musical instrument. The second playing mode is called the strum mode in which the strings are plucked in a sequence. The strum mode is difficult to imitate on a keyboard instrument because considerable dextral skill is required to sequence through six widely separated notes of a chord in a time sequence which is imitative of a guitar strum. Further complications arise because the guitar strum time is not constant but varies in such a manner that it introduces an emotional expression into the musical performance.
A mechanical-type problem is translated to a musical choice limitation when one closely examines the implementation of a keyboard musical instrument which realistically imitates a guitar. The only restriction on the input chord data entered by a keyboard is the simple ability to span and actuate a set of keyboard switches. Certain well-known limitations can occur between the raised black keys and the white keys. The guitar player is saddled with a different set of mechanical limitations in the placement of a set of fingers on the strings. These limitations are a product of the spacing of the strings, the spacing of the frets, and the prescribed open tuning of the strings. Not all chord combinations and their inversions which are possible to key on a keyboard instrument are equally possible to finger on a guitar.
In U.S. Pat. No. 3,967,520 there is described a system for imitating a guitar using a keyboard electronic musical instrument. A preferential keying matrix is employed to restructure a one hand chord into open harmony chords spanning a two octave range while maintaining each of the input notes of the chord. The disclosed system is intended to operate primarily as the accompaniment section for a keyboard instrument by being incorporated into the lower keyboard of an organ.